1. Field of the Invention
The present invention relates to a process and a device for connecting ends of a seam of extruded plastic material on a sheet of glass, particularly a windshield of an automobile, in which the seam of plastic material forms an edge gasket.
2. Description of the Prior Art
It is known that in order to reduce the cost associated with assembling a windshield to the body of an automobile, a process is used which consists of extruding directly onto the glass a polyurethane seam having a predetermined cross section, the polyurethane being polymerized by environmental humidity so as to form a gasket which adheres to the glass itself.
Assembling the windshield to the body of the automobile is greatly simplified, as it is sufficient to spread an adequate quantity of adhesive on the hardened seam, compatible with the polyurethane used to form the seam itself, and to stick the resulting sheet of glass onto the metal of the body.
In the manufacture of the seam it is necessary to provide the most suitable cross-sectional shape in order to meet requirements of resistance to vibration and sealing against the infiltration of water.
For ease of understanding, the following description will refer to a windshield of an automobile but it is obvious that the present invention can also be applied to any kind of fixed sheet of glass.
During the extrusion of the polyurethane material onto the sheet of glass, a calibrated nozzle is used, through which an amount of plastic material is delivered with pressure which, in correlation with the translational speed of the nozzle itself, defines the shape and thickness of the seam.
The problem to be solved according to the invention is that the seam has to be joined with itself, i.e. it is necessary to connect the starting end, or head, of the seam with the finishing end, or tail, in the best possible manner and using the least possible manpower.
The size of an extrusion nozzle forms a limit to the perfect union of the head and tail of the seam in that at the least a gap equal to the width of the nozzle itself will remain between the head and the tail. Furthermore the seam itself often has a cross section of a complex shape which is difficult to join up.
A typical complex shape is that made up of two sections connected one to the other, in which the first section rests completely against the glass and the second is cantilevered, connected to the first section at its one end only and projecting from the edge of the glass, as a notably elongate portion.
In this case it is difficult to obtain a mechanical connection because of the extrusion of the second projecting part which, due to the flowability of the polyurethane, is unable to maintain its shape during polymerization.